The present invention relates to a guide mechanism of a positioning device for a magnetic head moving apparatus.
In flexible ("floppy") disk storage systems in current widespread use, a recording/playback magnetic head must be accurately positioned relative to the center of rotation of the floppy disk in order to ensure compatibility between different floppy disks and floppy disk drives.
FIG. 1 is a top view of a magnetic head positioning apparatus with a conventional guide mechanism, and FIG. 2 is a sectional view taken on a line II--II in FIG. 1. In FIGS. 1 and 2, a magnetic head 1 for recording and playing back data is moved in the radial direction along the surface of a floppy disk 2, the magnetic head 1 being held by a movable base 3 forming a positioning device. The movable base 3 is constructed from engineering plastics by precision injection molding. Two bearings 5a, 5b having excellent slide properties are respectively fitted into holes 4a, 4b in holder devices 3a, 3b installed at opposite ends of the movable base 3. Specifically, bearings of self-lubricating Teflon or oil-impregnated sintered bearings 5a, 5b are press-fitted into the respective holes 4a, 4b or inserted therein with an adhesive, so that the bearings 5a, 5b are held on and incorporated with the movable base 3.
A guide bar 6 slidably passing through the bearings 5a, 5b constitutes a guide mechanism for the movable base 3. The magnetic head 1 coupled to one face of the movable base 3 is thus moved and positioned as desired by activating a driving motor 7 so as to cause it to rotate through a given displacement angle. Since such a positioning method and an arrangement can be implemented simply using a conventional mechanism, a detailed description thereof will be omitted. Briefly, however, a combination of a threaded shaft 7a and a bearing 3c engaged therewith may be employed. Supporting devices 6a, 6b are used to support the guide bar 6.
In the conventional magnetic head moving apparatus, an extremely high degree of precision is required for the holes 4a, 4b at the two ends of the movable base 3, specifically, for their inner diameter dimension (roundness if they are round holes) and their concentricity (alignment). As forming the movable base 3 completely of metal is costly, engineering plastic materials having a low deformability due to thermal shrinkage are selected to provide an inexpensive movable base 3 using precision injection molding.
However, it is difficult to make the holes 4a, 4b of the holder devices 3a, 3b truly round using ordinary precision injection molding techniques, and hence it is necessary to employ a specially shaped or complicated and expensive die for the injection molding process, or otherwise it is necessary to employ additional machining for correcting the dimensions of the holes 4a, 4b after an ordinary molding operation to attain the required precision of the inner diameter, roundness and concentricity. Consequently, the movable base 3 has been an expensive part.